1. Field of the Invention
This invention relates generally to nuclear reactors and more particularly, to assemblies and methods for coupling core spray line assemblies within such reactors in a repair.
2. Description of Related Art
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A core shroud or shroud typically surrounds the core and is supported by a shroud support structure.
Boiling water reactors have numerous piping systems, and such piping systems may be utilized, for example, to transport water throughout the RPV. For example, core spray piping may be used to deliver water from outside the RPV to core spargers inside the RPV and to cool the core. The core spray piping may be coupled to a thermal sleeve which may be slip fit into a RPV nozzle safe end.
Stress corrosion cracking (SCC) is a known phenomenon occurring in reactor components, such as structural members, piping, fasteners, and welds which are exposed to high temperature water. The reactor components may be subject to a variety of stresses. These stresses may be associated with, for example, differences in thermal expansion, the operating pressure needed for the containment of the reactor cooling water, and other stress sources, such as residual stresses from welding, cold working and other inhomogeneous metal treatments. In addition, water chemistry, welding, heat treatment and radiation can influence the susceptibility of metal in a component to SCC.
Reactor internal piping, such as thermal sleeves and core spray lines, may occasionally require replacement as a result of failure due to SCC. Replacing the core spray piping typically may include removing the core thermal sleeve from the RPV nozzle safe end. In the event a safe end requires replacement, the reactor must be shut down for maintenance and drained to an elevation below that of the safe end. The safe end is then removed and a replacement safe end is welded to the RPV nozzle. Thereafter, a replacement core spray line (external to the reactor) may be welded to the replacement safe end. Replacing a safe end is typically time consuming and costly, since such replacement generally requires a lengthy reactor outage of several days to a week or more.
It would be desirable to provide an assembly which facilitates replacing core spray lines without removing the reactor pressure vessel safe end. It also would be desirable to provide such an assembly which is easily removed and installed without the necessity of welding.